Cause of Huge Wyo. Refinery Spill Happened Before

A storage tank roof that sank at a Sinclair Oil refinery earlier this year and caused Wyoming's biggest spill in decades wasn't unprecedented: A storage tank roof also sank at the refinery in 2007.

Leaks in the pontoons holding up the floating roofs occurred before both incidents.

The May 3 spill of 2.73 million gallons of gasoline-grade fluid created a serious explosion risk next to the south-central Wyoming town of Sinclair, population 420. Most of the fluid was recovered soon after the spill, but some continues to be removed from wells at the refinery.

On Jan. 20, 2007, the roof covering a tank of crude oil elsewhere at the refinery sank. As would happen more than two years later, the sinking roof punctured the tank bottom and caused a spill, said refinery manager Mike Bellinger.

The Wyoming Department of Environmental Quality found out about the 2007 incident during an inspection that November. The Associated Press obtained a department report mentioning the incident through a records request.

The 2007 spill was much smaller, involving only a few barrels of oil, Bellinger said. An inspection afterward, he said, revealed that oil had leaked into the roof pontoons through defects in the weld where the pontoons attached to a bulkhead — a flaw that probably had existed for some time.

"It was probably an original manufacturer defect," Bellinger said.

An inspection six months earlier, he said, hadn't revealed any oil in the pontoons.

That wasn't the case with this year's roof sinking and spill. Some months before the accident, a contractor documented fluid inside two pontoons supporting the tank roof, Bellinger said.

The refinery lost track of the report.

"The records didn't get properly entered into our work order system," he said. "So there was kind of a failure in our management system in the plant and the problem of those two pontoons didn't get addressed quickly enough."